The invention relates to improvements in method and apparatus for the separation of a materials stream such as cement to different gradations of fine through coarse grained fractions. More particularly, the invention employs a rotatable distributing plate to form an annular bell shaped veil of material with separating air passing inwardly to fractionally separate the material.
Dispersion air classifiers for separating pulverulent materials in a stream into a plurality of fractions have been known such as, for example, in German AS No. 26 17 788.
In accordance with classification devices utilized, the material to be classified is distributed by a rotatable circular distributing plate which throws off the material in a bell shaped veil, and separating air is passed through the material in a radially inwardly direction. The coarse material is slung outwardly due to centrifugal force and also being acted on by the force of gravity, falls down along an outside wall of a classifying chamber into a conically shaped lower part of the classifier.
The separating air which is passed radially inwardly is loaded with finer grain fractions and is conducted inwardly by means of concentrically arranged air deflecting baffles. Additionally, grain fractions are discharged by forces of mass inertia at the reversing locations of the air and are collected in annularly arranged air conveying channels in order to be discharged as separated according to grain size categories.
Such classifiers are disadvantageous particularly when they are to be suitable for separating different grain size categories. They require large volumes and involve large expensive apparatus so that the cost for the apparatus and conveying means is expensive.
Commercial practice dictates that cement plates frequently operate in a part-load range. Currently the number of new plants being erected is relatively small. Therefore, technological development is primarily directed toward the optimization of existing systems. The goal of this optimization is to be able to produce a larger qualitatively different spectrum of products in the same systems in different quantities at favorable costs and in such a manner as to also possibly increase the capacity of the plants. The accommodation of the requirements of final grinding is also a subject matter of such efforts. Particular attention is paid to circulation of the material within the mill in order to improve the performance of the classifiers.
Accordingly, an object of the present invention is to obtain a method of classifying and a design of classifier mechanism which is suitable for the optimization of existing systems and avoids the disadvantages of heretofore known classifiers. Such classifier should be capable of a greater separation power in the same space or in a smaller space than traditional classifiers. Further, the classifier should be as easy as possible to integrate into the materials flow even in existing systems.
A further object of the invention is to provide a classifier which would enable the separation of a number of products and whereby its maintenance should be easy to carry out under the restricted conditions of existing systems. The installation of such classifiers should be possible in a simple way and with the minimum shut-down time of a plant during modernization.
In accordance with the principles of the invention, the objects are achieved by providing a rotating plate which rotates on a vertical axis such that material distributed on the center of the plate is centrifugally discharged radially outwardly and with the combination of the centrifugal force and the force of gravity, a bell shaped material veil is provided. An annular radially inwardly directed flow of separating air is passed through the veil of materials and the discharge of the separating air which is loaded with the finer grain fraction emerges centrally and downwardly and the coarser material is collected in an annular outwardly located chamber. By this method, the size of the product bell shaped veil can be arbitrarily adapted to the desired classifying capacity. The method allows a relatively large material stream to be classified in an advantageously small space. Further, it allows the materials flow to be fashioned especially advantageously relative to utilization of the force of gravity. It has been found that the occurring pressure losses and energy consumption are surprisingly low. The divergence of the separating air located with the finer grained fraction passing radially inwardly in the direction of the classifier axis allows a separation of the fine grain fraction in, for example, cyclones positioned directly below the classifier. The flow routes thereby become relatively short so that this reduces the energy consumption of the process. Collecting the coarser materials in an annular outwardly located space permits the provision of an eccentric coarse materials discharge.
The required airstream for the classifier can be kept surprisingly low due to the bell shaped materials veil. Changes in the classifier airstream will have a less disadvantageous influence on the classifier performance than in heretofore known classifying methods.
In accordance with the principles of the invention, the classifying air which is directed in an inwardly flow through the bell shaped veil is divided into classifying air substreams. Different substreams are loaded with different gradation of fine grade compositions. This accomplishes a particularly beneficial multi-product classification. Moreover, uniform wear, particularly of a distributor which is utilized can be achieved.
In accordance with a further function of the invention, a uniform distribution of classifying air is provided over the bell shaped material veil. That is, the classifying air is uniformly distributed relative to the veil before it passes through the material veil and thus an advantageously sharply defined separation boundary of the classifier is obtained.
It is a further feature of the invention that the classifying air is deflected before passing through the material veil particularly with a deflection which is differentially adjustable for each substream of the classifying air. The flow direction of the classifying air with reference to the material veil can be set in accordance with the deflection of the classifying air. Depending on the materials to be classified and upon the desired separating boundaries, the classifying air can be introduced into the material veil either more steeply or flatter or even tangentially as desired under the particular operating circumstances.
A further feature of the invention provides that a separate discharge of the substreams of classifying air loaded with different fine grained fractions can be used. That is, different fine grained fractions can be separated from the separately discharged substreams of classifying air with the utilization of known separating methods such as cyclones.
Further in accordance with the invention, the discharge of the classifying air occurs on the same axis and in the same direction as to the admission of materials into the classifier. As a result, the system parts can be easily arranged coaxially one above the other. In some instances this permits re-equipping mill structures of existing systems which are often limited in ground area but provide for substantial height.
A further feature of the invention is that it employs a symmetrical division and guidance of the classifying air before it is passed through the materials bell shaped veil. The division of the classifying air and symmetrical guidance allows short routes of airflow and a very compact structure for the classifier. This also accomplishes a further measure for reducing operating costs.
A further factor of the invention is that coarser material is pneumatically discharged from a surrounding annular space by feeding secondary air which is important particularly for raw material having residual moisture. The coarse material is mechanically discharged. By avoidance of a sole gravity discharge of the coarse material, this leads to a further reduction of the overall necessary volume. Dry material can be advantageously discharged trouble-free in pneumatic fashion. It is better to mechanically discharge coarse material having residual moisture.
A further factor of the invention is that dust-laden air is supplied such as from a mill de-dusting. This arrangement advantageously allows the costs for the de-dusting of other system parts to be reduced. Auxiliary apparatus for de-dusting air arising from mill de-dusting are avoided. The dust particles present in the air are separated from the classifying air in a separating device which is already present.
A further factor of the invention exists in that the finer grained fractions are classified in concentric substreams of classifying air having a grain size increasing from the inside toward the outside. A multi-product classification can thereby be implemented utilizing the same principles. Dependent upon which streams of fine material are combined, the method can be easily adapted to different quality demands of the final product. The method opens up the flexibility of being able to react in an extremely flexible way to market requirements and changes.
It is a further feature of the invention that a cooling of the coarse material is undertaken by means of secondary air. The coarse material can be cooled in this process stage at the same time by the introduction of secondary air, particularly as a medium for pneumatically conveying the coarse material. A concentric arrangement of the conveying channel relative to the fine product discharge as an annular channel allows the coarse material to be cooled over a relatively long path and on an adequately large surface.
A dispersion air classifier may be used for the implementation of the method particularly for classifying cement, and this dispersion air classifier comprises a material admission means, a distributing plate with a drive which rotates the plate and distributes the material stream centrifugally off the plate edge to form a materials veil, a rotatable distributor, a feed aperture for classifying air, and a coarse materials discharge with at least one fine materials discharge as well as the classifier axis which is essentially vertical, that is in the direction of the earth's gravitational field so that thereby the materials admission and the fine materials discharge are arranged around the classifier axis, and a conveying channel is arranged around the fine materials discharge for the coarse materials discharge. The material distributed by the rotary plate is passed through the classifying air as a bell shaped generated veil or fog. The combination of the foregoing features provides a classifier with a high classifying performance which has a relatively advantageously low overall structure. The material paths are unusually short and the fine materials discharge are arranged coaxial with the classifier axis which allows separating cyclones to be used when desired and to be arranged directly below the classifier. As a result of the small structural volume, the classifier can also be easily integrated into existing old systems. Further, this arrangement contributes to the increase in capacity. The coarse material is not centrally discharged but is advantageously discharged from an outward location from an annularly arranged conveying channel coaxial with the classifier. The materials stream which is distributed to form a bell shaped generated mist surface exhibits a large area in comparison to other heretofore known classifiers so that this accomplishes a classifier with an unexpectedly high classsifying performance in comparison to its structural volume.
In accordance with the invention, the classifier uses at least one classifying air distribution channel which is annularly shaped with variable or diminishing cross-section and has an air admission aperture with the axis extending perpendicularly to the classifier axis. The classifying air distribution channel allows the air to symmetrically flow from the air admission aperture to the materials veil on a very short path. The symmetrical parts advantageously simplify the manufacture of the classifier.
It is a further feature of the invention that the air distribution channel includes air discharge apertures whose exit axis are parallel to the classifier axis and are arranged concentrically distributed around the classifier axis. A twist-free and very uniform air distribution derives in this way. Moreover, this arrangement of air admission into the classifying chamber allows an especially compact structure of the classifier since the classifying chamber and air distribution channel are arranged one above the other accomplishing advantageously low outside diameters of the classifier.
A further feature of the invention resides in that the classifying air distribution channel is arranged above the classifying chamber which is fashioned as a truncated cone tapering toward the bottom. This shaping of the classifying chamber allows dust-laden classifying air to be employed. Dust particles are presented with no opportunity of forming disturbing deposits in the classifying chamber.
In accordance with the construction of the apparatus, a hood is employed having a diameter which is smaller than or the same as the inside diameter of the classifying air distribution channel and which is attached with a relesable connection. This effects a further reduction in the structural volume of the classifier. The inside diameter of the classifier air distribution channel also functions as a hood wall. After the connection is released, the wear parts can be advantageously withdrawn toward the top in a simple way and serviced. The structure of the classifier employs a distributing plate, a drive and hood which are fashioned to form an interrelated assembly unit. The assembly and maintenance are thereby advantageously reduced and further, the availability of the classifier for servicing, is increased.
The distributing plate employs a hollow drive shaft in which a conduit for the admission of the materials stream is arranged. The materials stream admission is thus designed in a particularly trouble-free way. Blockages within the admission conduit which sometimes occur with angled conduits are avoided and the wear is reduced. The seating of the distribution plate and of the distributor can be dimensioned large in an advantageous way.
Another factor of the invention is the drive which uses a gearing having a hollow shaft that is arranged to receive the materials stream admission and which has a wall that is coolable. Another even more compact structure of the classifier uses a gearing fashioned in this matter. The cooling design of the hollow shaft avoids injurious influence of the materials temperature on the transmission oil.
The structure of the invention utilizes one or more dip pipes or tubes coaxial with the classifier. For the separation of a plurality of grades of fines, a plurality of concentric tubes are employed and the fine material can flow directly down the individual tubes into collection apparatus for receiving the separated fine material. This effects a saving in machine size and capital costs.
The tubes employ classifying air dividing plates which extend radially horizontally and are concentrically arranged around the tubes with each tube having an air dividing plate attached to it and being adjustable in height. With the assistance of the tubes and the air dividing plates, the charging of air into the mechanism can be influenced. Wear of the distributor can be made uniform so that the maintenance intervals are lengthened. This feature contributes to the availability of the classifier. When the classifying air substreams are discharged downwardly separately into different tubes, a multi-product classification is possible with the same classifier thus permitting the dividing of the input materials stream into different grain size ranges. A parallel operation of a plurality of classifiers having different separating boundaries for the multi-product classification is not necessary. Overly involved structural engineering measures for multi-product classification are avoided.
In accordance with the invention which employs air, deflection and distribution elements in the classifying chamber, a vane ring is provided which is separately adjustable from the outside for each classifying air part. The management of the air flow and distribution of classifying air can be influenced by the integration of air, deflection and distribution profiles in the classifying chamber. The adjustment of these profiles can be fashioned with a vane ring of a type heretofore known which allows the separating boundary of the classifier to be adapted as desired. The separate adjustment of the vane ring for each substream of classifying air is advantageous in multi-product classification. The composition of the individual grain size ranges in the fine material can thereby be controlled. It is contemplated that for the removal of coarse material a mechanical conveyor may be employed such as a scraper flight conveyor utilizing clearing paddles. Pneumatic discharge of the coarse material becomes difficult if the material has residual moisture. A mechanical conveyor can be employed obtaining particular advantage with such material. Scraper flight conveyors which operate without a slope further advantageously reduce the overall height of the classifier. Clearing paddles can be structurally united with the distributor in a simple way. With rapid running of the distributor, the coarse material is again hurled into the classifying airstream by the clearing paddles and the classification favorably influenced.
The classifier employs an air conveyor channel having slopes down to a coarse materials discharge. Air conveying channels are operationally reliable particularly in systems for the manufacture of cement. The introduced secondary air can be simultaneously used for cooling the discharged coarse material. However, air from the de-dusting circulations can also be employed as secondary air so that existing de-dusting systems are used to a lesser degree and need not be provided in given new systems. The structure can be provided with blow-off jets for the distributor. Layers of fine material which have built up can be removed from the distributor in a particularly easy and efficient way. These jets can be combined with the paddles of the distributor which results in the pneumatic removal of layers of fine material. A quiet running of the distributor is achieved over long operating times.